“I want to congratulate Hillary Clinton on making history as the presumptive democratic nominee for president of the United States,” Obama said in a three-minute video posted by the Clinton campaign. “I don't think there's ever been someone so qualified to hold this office.”

The president also thanked Bernie Sanders and stressed their desire to unify the party in the wake of a divisive primary battle.

The president recorded the video on Tuesday, White House Press Secretary Josh Earnest told reporters. Obama informed Clinton of his decision that night.

“I've seen her determination to give every American a fair shot at opportunity, no matter how tough the fight was. That's what has always driven her and it still does,” Obama continued. “So I want those of you who have been with me from the beginning of this incredible journey to be the first to know that I'm with her. I am fired up and I cannot wait to get out there and campaign for Hillary.”

Obama will hit the campaign trail to support Clinton next week, appearing with her in Green Bay, Wisconsin, on June 15.

It is rare for a sitting president to be both willing to campaign on behalf of his party's chosen successor and popular enough for that candidate to welcome his support. President George W. Bush's low approval ratings were seen as a liability for Sen. John McCain in 2008, and while President Bill Clinton was popular at the end of his second term in 2000, Vice President Al Gore opted to distance himself from his boss due to the scandals swirling around Clinton.

“It just means so much to have a strong, substantive endorsement from the president," Clinton said in an interview with Bloomberg Politics tied to the video's release. "Obviously I value his opinion a great deal personally. ... It’s just such a treat because over the years of knowing each other, we’ve gone from fierce competitors to true friends.”

Obama's endorsement comes just days after Clinton crossed the threshold of delegates necessary to secure the Democratic nomination. The president dedicated much of his endorsement video to praising Sanders and insisting that his populist message would deeply inform the party's platform going forward.

“I know some say these primaries have somehow left the Democratic Party more divided,” Obama said in the video. “Well, they said that eight years ago as well. But just like eight years ago, there are millions of Americans, not just Democrats, who've cast their ballots for the very first time. And a lot of that is thanks to Senator Bernie Sanders, who has run an incredible campaign.”

“Embracing [Sanders's] message is going to help us win in November," Obama added. "But, more importantly, it'll make the Democratic Party stronger, and it will make America stronger."

Sanders has yet to drop out of the race, saying he plans to compete in next week's final primary, in Washington, D.C. He may even take his campaign all the way to the Democratic National Convention next month in Philadelphia.

In a press conference after a meeting with Obama on Thursday, Sanders sounded a conciliatory note about his Democratic rival but stopped short of endorsing her. He did, however, pledge to do whatever he could to prevent the “disaster” that would occur if Trump won in November.

"I am going to do everything in my power, and I will work as hard as I can, to make sure that Donald Trump does not become president of the United States,” Sanders said after the meeting. "I look forward to meeting with...[Clinton] in the near future to see how we can work together to defeat Donald Trump and to create a government which represents all of us and not just the one percent.”

But when a reporter asked Sanders about Obama's just-released endorsement of Clinton as Sanders sat with Senate Minority Leader Harry Reid, Sanders repled with awkward silence.

In the aftermath of violence at a Donald Trump rally last week, Trump supporters on websites like 4chan and Stormfront say they've revealed the identity of one protester now famous for tackling a Trump supporter on live television.